This invention relates to a compact refractor optical system and more particularly, relates to a refractor having a test axis folded at least twice.
It is frequently desirable to position a movable member at a specified location relative to an object. One art in which such alignment is frequently practiced relates to ophthalmic instruments. Usually, ophthalmic instruments such as slit lamps, contact tonometers, and the like used the same optical system for positioning a movable portion of the instrument as that used for observing (slit lamps) or to measure (tonometers).
Subjective refractors, optometers, which present a target image for viewing by a patient are known.
U.S. Pat. No. 3,785,723 issued Jan. 15, 1974, to Guyton relates to a method of testing the eye for astigmatic error and diagrammatically describes an optical arrangement in FIG. 7. The system has a combined spherical and cylindrical unit for selective varying sphere and/or cylinder power.
U.S. Pat. No. 3,664,631 issued May 23, 1972, to Guyton further describes the sphere and cylinder lens unit, and variations thereof.
U.S. Pat. No. 3,842,254 issued Oct. 15, 1974, to Dianetti, and U.S. Pat. No. 3,832,890 issued Sept. 3, 1974, to Grolman et al, are examples of ophthalmic instruments having alignment systems in which the operator's head follows movement of the instrument during alignment.